The present invention relates to a semiconductor designing technology, and more particularly, to a semiconductor memory device for receiving a data strobe signal of a data transmitted thereto and performing a data write operation.
In general, semiconductor memory devices including Double Data Rate Synchronous Dynamic Random Access Memory (DDR SDRAM) use data strobe signals to accurately recognize input data. Data strobe signals are signals outputted along with a data from a chipset and toggling according to the data. Data and external clock signals are transferred from a chipset to the semiconductor memory device through different transmission lines and the difference in the transmission rates of the different transmission lines may cause a data recognition error. Therefore, a chipset transfers a data strobe signal to a semiconductor memory device through a transmission line similar to a transmission line through which a data is transmitted. The semiconductor memory device can accurately recognize the data by using the data strobe signal transferred through the similar transmission line. Herein, the data strobe signal should be secured with setup time and hold time, and it includes a pair of a first data strobe signal and a second data strobe signal. The second data strobe signal is a signal obtained by inverting the first data strobe signal.
FIG. 1 is a block diagram illustrating a typical system structure. Referring to FIG. 1, the system includes a chipset 110 and a semiconductor memory device 130.
The chipset 110 outputs a data DAT, a first data strobe signal DQS, a second data strobe signal /DQS, which is an inverted signal of the first data strobe signal DQS, a first external clock signal CLK, and a second external clock signal /CLK, which is an inverted signal of the first external clock signal CLK, to the semiconductor memory device 130. Herein, the data DAT, the first and second data strobe signals DQS and /DQS, and the first and second external clock signals CLK and /CLK are outputted through corresponding transmitters 112A, 112B and 112C, respectively.
The semiconductor memory device 130 includes a plurality of receivers, which are first to third receivers 132A, 13213 and 132C in the drawing, for receiving output signals of the transmitters 112A, 112B and 112C of the chipset 110, respectively. Herein, the output signals of the transmitters 112A, 112B and 112C are terminated and transferred with a voltage level swinging within a small range based on a termination level. The transferred signals have a voltage range corresponding to power source voltage at outputs of the first to third receivers 132A, 132B and 132C. This signal transfer operation is performed through first and second resistors R1 and R2 connected to output terminals of the transmitters 112A, 112B and 112C and third and fourth resistors R3 and R4 connected to the input terminals of the first to third receivers 132A, 132B and 132C. Herein, the first resistor R1 and the second resistor R2 have the same resistance value and the third resistor R3 and the fourth resistor R4 have the same resistance value in order for the first to fourth resistors R1, R2, R3 and R4 to perform the termination operation.
Meanwhile, a first receiver 132A receives a signal corresponding to the data DAT and transfers an output signal to a first synchronizer 150 through a first delayer 134A. A second receiver 132B receives a signal corresponding to the first and second data strobe signals DQS and /DQS and outputs a signal. The output signal of the second receiver 132B is controlled by a ring-back controller 134B and transferred to the first synchronizer 150. Herein, the first delayer 134A compensates the output signal of the second receiver 132B for a delay time corresponding to a delay time of the ring-back controller 134B.
The ring-back controller 134B removes a glitch phenomenon of a falling data strobe signal DQS_F generated due to noise added to the first and second data strobe signals DQS and /DQS. The glitch phenomenon of a falling data strobe signal DQS_F and detailed circuit and operation of the ring-back controller 134B will be described again hereinafter with reference to FIGS. 5 to 7.
The first synchronizer 150 synchronizes an output signal of the first delayer 134A with an output signal of the ring-back controller 134B. The first synchronizer 150 is in charge of synchronizing the data DAT with the first and second data strobe signals DQS and /DQS. An output signal of the first synchronizer 150 is transferred to a second synchronizer 170, and a third receiver receives a signal corresponding to the first and second external clock signals CLK and /CLK and outputs a signal. The output signal of the third receiver 132C is transferred to the second synchronizer 170 through a second delayer 134C. Herein, the second delayer 134C includes a delay circuit for securing tDQSS defined based on a specification and a delay circuit for compensating for the time when a clock signal is delayed for synchronization operation in the ring-back controller 134B.
Meanwhile, the second synchronizer 170 synchronizes the data that is synchronized with the first and second data strobe signals DQS and /DQS with clock signals outputted from the second delayer 134C and outputs internal data INN_DAT. In other words, the second synchronizer 170 synchronizes the data synchronized with the first and second data strobe signals DQS and /DQS with the first and second external clock signals CLK and /CLK.
FIG. 2 is a waveform diagram describing operation waveforms of signals outputted from the chipset 110 shown in FIG. 1. Referring to FIG. 2, the chipset 110 simultaneously outputs the first data strobe signal DQS and the data DAT to the semiconductor memory device 130 during a write operation. Herein, the first data strobe signal DQS and the data DAT maintain the initial termination level. The data DAT are outputted in a sequence of R0, F0, R1, F1, R2, F2, R3 and F3 to correspond to the first and second data strobe signals DQS and /DQS, respectively. The first data strobe signal DQS and the data DAT maintain the termination level except for a pre-amble section and a section where the data DAT are transferred.
FIG. 3 illustrates the first receiver 132A and the second receiver 132B of FIG. 1 in detail. Referring to FIG. 3, the first receiver 132A receives a data DAT and a reference voltage VREF, performs buffering on them, and outputs a signal iDAT of a logic level corresponding to the buffering result. Herein, the data DAT is inputted to a positive (+) terminal of the first receiver 132A while the reference voltage VREF is inputted to a negative (−) terminal.
Subsequently, the second receiver 132B generates a rising data strobe signal DQSR_R and a falling data strobe signal DQS_F in response to the first and second data strobe signals DQS and /DQS. The second receiver 132B includes a receiver 310 for a rising signal and a receiver 330 for a falling signal. The receiver 310 for a rising signal receives the first data strobe signal DQS through a positive (+) terminal and the second data strobe signal /DQS through a negative (−) terminal and performs buffering on them to thereby generate a rising data strobe signal DQSR_R. The receiver 330 for a falling signal receives the second data strobe signal /DQS through a positive (+) terminal and the first data strobe signal DQS through a negative (−) terminal and performs buffering on them to thereby generate a falling data strobe signal DQSR_F.
FIG. 4 is a waveform diagram describing input and output signals of the receiver 310 for a rising signal and the receiver 330 for a falling signal. As illustrated in FIG. 4, the first data strobe signal DQS and the second data strobe signal /DQS are inputted with an opposite phase to each other. Herein, the receiver 310 for a rising signal generates a rising data strobe signal DQSRR corresponding to the first data strobe signal DQS, while the receiver 330 for a falling signal generates a falling data strobe signal DQS_F corresponding to the second data strobe signal /DQS.
Meanwhile, the waveforms of FIG. 4 show an ideal case where noise does not occur in the first and second data strobe signals DQS and /DQS.
FIG. 5 is a waveform diagram illustrating a case where a glitch phenomenon occurs in the first and second data strobe signals DQS and /DQS of FIG. 4. Referring to FIG. 5, a noise component, such as power noise, may be added to the first and second data strobe signals DQS and /DQS to thereby generate ring-back noise marked as {circle around (1)} in the drawing. In this case, the rising data strobe signal DQS_R and the falling data strobe signal DQS_F cause the glitch phenomenon marked as {circle around (2)}. The glitch phenomenon induces a malfunction of the semiconductor memory device 130. Therefore, the ring-back controller 134B is provided to remove the glitch phenomenon.
FIG. 6 illustrates the ring-back controller 134B of FIG. 1. Referring to FIG. 6, the ring-back controller 134B includes a command decoding unit 610, a repeating unit 630, a shifting unit 650, a delay unit 670, and an output unit 690. The command decoding unit 610 decodes an external command signal CMD and generates a write pulse signal WT_P. The repeating unit 630 amplifies a first external clock signal CLK. The shifting unit 650 shifts the write pulse signal WT_P in response to a clock signal outputted from the repeating unit 630. The delay unit 670 delays a falling data strobe signal DQS_F and outputs a delayed falling data strobe signal D_DQS_F. The output unit 690 generates a final falling data strobe signal FIN_DQS_F in response to a strobe control signal DIS_DQS outputted from the shifting unit 650 and the output signal D_DQS_F of the delay unit 670.
Herein, the shifting unit 650 includes a plurality of flip-flop and the last flip-flop of the shifting unit 650 outputs a signal inputted from the previous flip-flop as the strobe control signal DIS_DQS in response to the output signal D_DQS_F of the delay unit 670.
FIG. 7 is a waveform diagram illustrating major signals of the ring-back controller 134B shown in FIG. 6. Referring to FIG. 7, a ring-back effect occurs in first and second data strobe signals DQS and /DQS as shown in {circle around (1)}, and the glitch phenomenon occurs in a falling data strobe signal DQS_F as shown in FIG. 5. The glitch phenomenon also occurs in a delayed falling data strobe signal D_DQS_F outputted from the delay unit 670 of FIG. 6 as shown in {circle around (2)}.
Meanwhile, when a write command is applied through an external command signal CMD, a write pulse signal WT_P is activated. Generally, the pulse width of the write pulse signal WT_P corresponds to a cycle of the first external clock signal CLK. The write pulse signal WT_P is shifted in the shifting unit 650 and outputted as a signal DIS_P in response to the first external clock signal CLK. Herein, a signal outputted from the last flip-flop of the shifting unit 650 is synchronized with the delayed falling data strobe signal D_DQS_F. In other words, the write pulse signal WT_P is synchronized with the external clock signal CLK, shifted, finally synchronized with the delayed falling data strobe signal D_DQS_F, and outputted as a strobe control signal DIS_DQS. Finally, the delayed falling data strobe signal D_DQS_F is logically combined with the strobe control signal DIS_DQS to become the final falling data strobe signal FIN_DQS_F. The final falling data strobe signal FIN_DQS_F becomes free of the glitch phenomenon by the strobe control signal DIS_DQS.
Herein, a glitch removing operation is not performed onto a rising data strobe signal DQS_R because there is a margin as much as almost a cycle between a rising edge of a rising data strobe signal DQS_R and a rising edge of a clock signal inputted to the second synchronizer 170. In case of a semiconductor memory device having a low operation frequency, it does not have to remove the glitch phenomenon occurring in the rising data strobe signal DQS_R. However, in the circumstances that the operation frequency of a memory device increases, which is the current trend, the glitch phenomenon of the rising data strobe signal DQS_R may also induce a malfunction as well.
Although not illustrated in the drawing, the glitch phenomenon may occur before a pre-amble section. The glitch phenomenon causes a malfunction of receiving a data before a desired time point on the part of the semiconductor memory device 130.
Meanwhile, the output signal DIS_P obtained after shifted in response to the first external clock signal CLK is synchronized with the delayed falling data strobe signal D_DQS_F. To make the synchronization operation performed smoothly, the delay time of the output signal DIS_P obtained after shifted should be the same as the delay time of the delayed falling data strobe signal D_DQS_F. To make the delay times the same, a delay circuit is added. The additional delay circuit should be additionally designed in the second delayer 134C as well to secure tDQSS, and this works as a factor for increasing a chip area of a semiconductor memory device.
However, although the delay circuits are added, it is substantially difficult to make the delay times of the output signal DIS_P obtained after shifted and the delayed falling data strobe signal D_DQS_F the same. Also, since the positions of the delay circuits are different, the delay amount of each delay circuit may differ according to a process, voltage, temperature and the like and this makes it hard not only to perform a synchronization operation between the output signal DIS_P obtained after shifted and the delayed falling data strobe signal D_DQS_F but also secure the tDQSS. After all, when the synchronization is not performed at a desired time point, there is a problem in that the glitch phenomenon caused by the ring-back effect of the first and second data strobe signals DQS and /DQS, and when the tDQSS is not secured, the semiconductor memory device performs a malfunction in that it does not recognize a desired data properly.